Olive leaf extract is a supplement derived from the leaves of the plant that bears olive (a fruit from which the cooking oil is derived from) and contains the main bioactives of hydroxytyrosol/tyrosol and oleuropein/ligstroside.
Olive phenolics in general, which are present in high levels in olive leaf supplements, appear to potently protect against the oxidation of LDL cholesterol. This is attributed to the effects of hydroxytyrosol, and appears to be active at a low enough dose to apply to olive product (e.g., extra virgin olive oil) consumption. Olive leaf may also influence levels of blood lipids in a beneficial manner (lower LDL-C, lower triglycerides, higher HDL-C) although these changes are rather small and inconsistent. Olive leaf extract shows some promise in lowering blood pressure in people with high blood pressure.
Olive leaf extract may have beneficial effects on glycemic control, although research is limited. The mechanisms of olive leaf on glucose metabolism could be related to effects on pancreatic function and/or inhibition of carbohydrate (e.g., sucrose) metabolism in the intestines.
Although olive leaf has been implicated in fat burning through various mechanisms (increased thyroid hormones and adrenaline have been shown in animal studies), clinical trials have failed to show a fat burning effect with olive leaf supplement use. The reason for this is not known, but may be related to a decrease in levels of the receptor that adrenaline works through which may attenuate the effects.
